A reaction takes place in various steps. The rate constant for first, second, third and fifth steps are \[{{k}_{1}},{{k}_{2}},{{k}_{3}}\] and \[{{k}_{4}}\] respectively The overall rate constant is given by \[k=\frac{{{k}_{2}}}{{{k}_{3}}}{{\left( \frac{{{k}_{1}}}{{{k}_{5}}} \right)}^{1/2}}\]. If activation energy are 40,60,50 and 10 kJ/mol respectively, the overall energy of activation (kJ/ mol) is:

• A. 10  
• B. 20
• C. 25                                
• D. none of these